Production of butadiene



Patented Feb. 29, 1 944 ouvei? wJ-c a sjs,,1vmgitmflun .1min,v assignorto E. 1., dufilontde Nemonrs-hjcomnmiw l- .SerialNo.353,543 "1 MM) Thisvrelates to the production of butadiene from butane or butylene." Anobject of this invention is to provide an improved methed for producingbutadiene from a process which involves pyrolysis of a dihalobutane.Another object is to carry out such process whileiavoiding theproduction of halogenated by-products and in such'manner as to avoidloss of halogen. Other objects will be apparent from the followingdescription of the invention.

In accordance with the present invention dibrombutane is prepared bybromination of hutylene. The dibrombutane thenis heated to a suitablecracking temperature which results in the formation of a gaseousmixtureof butadiene and hydrogen bromide. The hydrogen bromide is separatedfrom this mixture by any suitable known means, for example, byfractional distillation at temperatures below the boiling pointofbutadiene. The hydrogen bromide vapor thus recovered is oxidized byreaction with oxygen,

' preferably in the presence of a suitable oxidado not react with thebromine. From this Junreacted gaseous residue the hydrogen is sepa 1rated from the butane by low temperature distillation and the butane isre-cycled to the pyrolysis I operation.

The dibrombutane obtained by the above 'pro-.-' cedure isflrsttreated'to remove the water'prescut and then iss'ubiected to pyrolysisat a temperature of 350 to 600 C., preferably between 450 and 500 C.,which causes it 7 to, decompose to form butadiene and hydrogen bromide.The of!- gases from the pyrolysis are cooled to a temperation catalyst,to convert the hydrogen bromide to bromine. The product from theoxidation reaction consistsjof bromine and water vapors; it may alsocontain more or less of non-oxidized hydrogen bromide vapor, dependingupon the efllciency of the oxidation process. On condensation of thesevapors the liquid bromine and water separate into two layers. To theselayers is added suflicient chlorine to convert all the unoxidizedhydrogen bromideto bromine, and the combined layers are then utilized tobrominate a further quantity of butylene and the cycle is repeated. Theentire process may be carried out continuously to produce butadiene inexcellent yields and with substantially no loss of bromine.

In a preferred method of operating this process, butane is subjected topyrolysis to produce a gaseous mixture of butylene and hyrlrogemto-vgether with some unreacted butane. This mixturebelowthe boiling point ofbutadiene, and rectified to separate the hydrogen bromide from; thebutadiene. The hydrogen bromide then is mixed with sumcient air oroxygen tooxidize it to water and bromine. The hydrogen bromide- 7 airmixtureis passed over a copper catalyst at a temperature of 200-400 C.,preferably around 300 C.,"to produces. gaseous mixture of bromineandwater vapor, which may contain, e. g., up

to byvolume of'unreacted hydrogen bromide. v

The vapors from the oxidation reac'tionare condensed at a temperaturebelow the boiling point of bromine, to produceliquid condensate whichseparates to form a layer of liquid bromine and a'supernatant waterlayer. Hydrogen bromide present will be dissolved in the water layer.The condensation temperature preferably is about 0 to C. Sufficientchlorine is added to the wature is passed intocontact with a liquidbromine and water mixture. For example, the pyrolysis gases may bepassed upwardly through a scrubbing tower counter-current to adownwardflow oi? the liquid bromine and water mixture. All of the'butylene' fromthe gas mixture reacts with the bromine to form dibrombutane, so that amixture of dibrombutane and water collects at the bottom of the tower orreaction-vessel. This reaction iscarriedout at a relativelylowtemperature and in the absence of light, for exampic at a maximumtemperature of 50 C., preferably at 20-30" C. Underthese conditions thebutane and the hydrogen in the pyrolysis gases ter layer to react withany hydrogen bromide present to form bromine and hydrogen chloride.Without further treatment, the liquid brominewater mixture is recycledto react with the butylene as described above.

The reactions occurring in this process may (3) cimBmcim- -zmsr(pyrolysis) v butadiene, the crude'butadiene may contain some.

unconverted dibrombutane and some monobrombutylene. Any unconverteddibrombutane and monobrombutylene in the crude butadiene may be readilyseparated by fractionation. These by-products when separated then may berecycled to the'pyrolysis step, whereby the dibrombutane andmonobrombutylene are converted to butadiene. There may also be formed inthe pyrolysis some small amountiof high boiling residuescontaining-bromine. From these residues the bromine may be recovered andrecycled by 2 a,ses,1 oe

feeding the residues into a gas or oil heme. and

scrubbing the gases from this time with water to absorb the hydrogenbromide produced. I'rom this wash watenbromine may be by treatment withchlorine, end re ed,

By the hereineserlbed invention it is possible;

to. obtain butodiene of hill: purity and in exodlent yields. Byoxidizing the hydrogen bro- A cyclic (or making bnte'diene' yhiehcomprises subjecting normel butener topyrol yxis to produce e zsseousmixture of butylene, hy-

.- -u endhy'drogenehloride; endthenreeotingemixdrogen end unchangedbutane. passing-said naeous mixture oounter-current-io e descendingstream of n mixed condensate consisting of liq uid bromine end water At.e 'tempereture not to dibrombutane; ooilecting the resultingunreeeted-mixture oi butene end hydrogen. seventing hydrogen thereiromand mold!!! the residuel butane to the xioreseid pyrolysis; heating thedibrombutone to a temperature of 450 to 500 C. to produce a.otgbutediene and hydrogen bromide; updating the hydrogen bromideendreecting it with oxygen at e tempereture o! 290to400C.inthepresence'oteooppereetelyst to to produce mixed vepors of elementalbromine end water: condensing sold mixed vepors to produee lim'ndbromine end mmin seperete leyedding chlorine to the water lsyer toeonvert on hydrogen bromide pruent to bromine tore oi said liquidbromine end water leyerswith the oi butene pyrolysis. es xioreseid.

OLIVER W. CASS.-

